Method for controlling the ignition time in internal combustion engines

ABSTRACT

An internal combustion engine gas exhaust device comprising an exhaust manifold ( 1 ) attached to the cylinder head for collecting exhaust gases driven out of the cylinders, and an exhaust line ( 8 ) comprising pollutant removing and sound absorbing means. The manifold ( 1 ) is connected to the exhaust line ( 8 ) via a coupling system ( 9 ) having a flange ( 10 ), a mating flange ( 11 ) and a gasket ( 12 ) therebetween. The flange ( 10 ) integral with the exhaust manifold ( 1 ) and/or the mating flange ( 11 ) integral with the exhaust line ( 8 ) is (are) shaped in such a way that the gasket ( 12 ) is protected from the exhaust gases.

[0001] The invention relates to a method for controlling the ignitiontime in internal combustion engines.

[0002] Modern internal combustion engines 1 (FIG. 1) have electronicignition systems which use a crankshaft angle sensor 2 to measure theangular position of a crankshaft 3 with regard to the upper dead centerof the piston. These ignition systems determine the ignition time bymeans of a predetermined angular position of the crankshaft, i.e.ignition of a fuel/air mixture which has previously been fed into thecombustion space 4 is triggered at the predetermined angular position.These ignition systems are as a rule a component of an electroniccontrol device of the internal combustion engine which also controls thefeeding in of the fuel/air mixture which is fed to the combustion space4 at an “earlier” or preliminary angular position.

[0003] In intake engines and conventional low-pressure injectiondevices, the time period which is necessary for feeding in the fuel/airmixture corresponds to a considerable crank angle range. The time forthe feeding in of the mixture is triggered, as is the ignition time, ata predetermined angular position of the crankshaft, but in simplecontrol devices the time of the start of the feeding in of the mixtureis not determined as precisely as the ignition time, since it is assumedthat the combustion is influenced essentially by the ignition time and,owing to the long period of feeding in fuel, it is not necessary todetermine precisely the start of the feeding in of fuel.

[0004] In internal combustion engines 1 having an injection device 10,it is customary to use a single control device 9 to control both theinjection process and the ignition time. In high-pressure injectiondevices, the fuel, or the fuel/air mixture, is fed to the combustionspace 4 in significantly shorter time ranges so that, when suchhigh-pressure injection devices are used, in particular with a directinjection of the fuel into the combustion space 4, the time of theinjection process, tog is determined precisely and is triggered at apredetermined angular position of the crankshaft. The precisemeasurement of the angular position of the crankshaft, both for theinjection process and for the injection time, constitutes a considerablecomputational outlay for the control device 9, the measurement processhaving to be carried out twice within a very short time.

[0005] High-pressure injection devices which operate according to theenergy storage principle are known, for example, from WO 92/14925 and WO93/18296. These high-pressure injection devices are used to inject thefuel into the combustion space in very short pulses. In addition, thereare high-pressure injection devices which operate according to thesolid-state energy storage principle, so-called “PNS (pump/nozzlesystems) injection devices” which are described, for example, in theGerman Patent applications P 195 15 781 and P 195 15 782. These PNSinjection devices are provided in particular for directly injecting thefuel into the combustion space, it being possible for the time periodfor an injection process during idling to be shorter than half amillisecond. The crankshaft angle sensor 2 which is used for measuringthe angular position of the crankshaft is composed of a toothed disk 5with teeth 6 arranged on the circumference, and a sensor element 7 whichis arranged at the circumferential region of the toothed disk 5 andsenses the passing through of the teeth 6 and converts it into anappropriate electrical pulse signal. The electrical signal is fed to thecontrol device 9 with a line 8. At high rotational speeds, the signal ofthe crankshaft angle sensor 2 has a high time resolution since the timeintervals between the passing through of two successive teeth 6 at thesensor element 7 are very short. On the other hand, these time intervalsare long at low rotational speeds (for example <2000 rpm), such as occurduring idling, so that the measurement of the rotational speed becomesimprecise, in particular if the rotational speed changes during themeasurement, since a change in the rotational speed between the passingthrough of two successive teeth 6 cannot be sensed precisely using thecrankshaft angle sensor 2. Such changes in rotational speed occur, forexample, during unsmooth idling, so that the measuring errors in themeasured rotational speed do not yet solve in an optimum way the problemof the correction to an idling desired-rotational-speed. The measuringerrors cause high fuel consumption resulting in relatively high emissionof pollutants.

[0006]FIG. 2 shows the rotational speed of an internal combustion engine[rpm] over the time period of one crankshaft revolution [s]. It emergesfrom this that at low speeds changes in the rotational speed bring abouta large change in the revolution time and thus great inaccuracies in themeasurement of the rotational speed and large measuring time errors.

[0007] U.S. Pat. No. 3,892,207 discloses an internal combustion enginewhich has a control device for driving the injection process and theignition by means of a single signal source. This control devicecontrols the injection and the ignition with a constant timing ratioindependently of the engine speed. The start of the injection and of theignition are separated by a predetermined time interval which ismeasured by a time delay device which operates independently of theengine speed. This method for determining the ignition time is appliedover the entire rotational speed range and it should be possible toapply it even in internal combustion engines which have higherrotational speeds than those of motor vehicles.

[0008] U.S. Pat. No. 4,621,599 discloses a method for injecting aquantity of fuel into a combustion space of an internal combustionengine and igniting it, in which method in each case a predeterminedquantity of fuel for ignition is injected into the combustion space at aspecific angular position of the upper dead center, and this quantityfor ignition is ignited at the same time or with a specific delay. Anadditional quantity of fuel is injected with a time interval withrespect to the quantity for ignition, which quantity is somewhat reducedin the case of a low load. In the case of a relatively large load, anadditional quantity of fuel is injected in advance of the upper deadcenter by a specific angular position. As a result of the provision of aplurality of injection pulses, the injection method is very complex inits configuration and requires considerable control expenditure.

[0009] The invention is based on the object of providing a method forcontrolling the ignition in internal combustion engines, which methodcan be implemented with simple means and yet can be applied over theentire rotational speed range of the internal combustion engine, bringsabout a high degree of smooth running particularly at low rotationalspeeds, especially when idling, gives rise to a very good level ofefficiency and considerably reduces the emission of pollutants.

[0010] The object is achieved by means of a method having the featuresof claim 1. Advantageous refinements are defined in the subclaims.

[0011] According to the invention, the ignition time is triggered belowa predetermined load threshold or rotational speed threshold if apredetermined time period has passed since the triggering of theinjection process. In order to carry out the ignition, it is not theangular position of the crankshaft in the region below the predeterminedload threshold or rotational speed threshold which is measured, butrather the expiry of a predetermined time period since the triggering ofthe injection process. This ensures that at the ignition time the fed-infuel/air mixture is in a predetermined state in which it can easily beignited. The measuring inaccuracies occurring at low rotational speeds(<2000 rpm) when the ignition time is being determined as a function ofthe crankshaft position are avoided, since the ignition time isspecified only as a function of the injection process so that verysmooth idling is achieved.

[0012] Above the load threshold or rotational speed threshold theignition time is determined in a manner known per se by measuring apredetermined angular position of the crankshaft, as a result of which aspecific relationship between the crankshaft angle of the upper deadcenter and the ignition angle can be maintained precisely in a simpleway.

[0013] The method according to the invention can be implemented usingvery simple technical means and achieves sensational synchronism inidling mode so that a two-stroke internal combustion engine can idlesmoothly even at a rotational speed of 180 rpm.

[0014] The method according to the invention can be applied in allinternal combustion engines having injection devices in which the fuel,or the fuel/air mixture, is fed to the combustion space with apredetermined time sequence, i.e. the injection process is atime-invariant process, the time period of which depends only on a fewparameters, for example the quantity of fuel injected per injectionprocess.

[0015] The invention is explained by way of example below with referenceto the drawing, in which:

[0016]FIG. 1 is a schematic view of a cross section of a cylinder of aninternal combustion engine having ignition and injection devices,

[0017]FIG. 2 shows the relationship between the rotational speed [rpm]and the crankshaft revolution time [s] in a diagram,

[0018]FIG. 3 is a schematic view of an injection device operatingaccording to the energy storage principle,

[0019]FIG. 4 is a cross section through a cylinder head and an upperregion of a piston which are designed for a direct injection and adirect ignition of the fuel,

[0020]FIG. 5 shows a cross section through a cylinder head and an upperregion of a piston which are designed for a direct injection of thefuel,

[0021]FIG. 6 shows a circuit which is used as a timer element formeasuring the predetermined delay time.

[0022] The method according to the invention has been applied to atwo-stroke internal combustion engine with two cylinders. The cubiccapacity of this internal combustion engine is 380 cm³ and the power is60 PS at 6500 rpm.

[0023] The injection device used is an injection (PNS) device operatingaccording to the solid-state energy storage principle, such as isdescribed for example in the German Patent Applications P 195 15 781 andP 195 15 782.

[0024] The basic principle of an injection device operating according tothe energy storage principle is illustrated schematically in FIG. 3.This fuel injection device is based on a piston pump 11 withelectromagnetic drive for sucking in fuel from a reservoir vessel 12 andfor accelerating the sucked-in fuel in a ram pipe 13, which is connectedvia a pressure line 14 to an injection nozzle 15. In addition, ashut-off valve 16 is arranged in a branch between the ram pipe 13 andthe pressure line 14, said shut-off valve 16 being designed as anelectromagnetic valve and controlling the passage of fuel to a returnline 17 which is connected to the shut-off valve 16 and opens into thereservoir vessel 12. The shut-off valve 16 and the piston pump 11 aredriven via the common electronic control device 9 which is connected tothe exciter coil of the shut-off valve 16, which is designed as asolenoid valve, and to a coil of the drive solenoid of the piston pump11. In addition, a nonreturn valve 19 is arranged in an intake line 20which connects the pump-side end of the ram pipe 13 to the reservoirvessel 12.

[0025] The piston pump 11 comprises a solenoid pump 21 having anarmature 22 which is arranged in the coil passage and is designed as acylindrical body, for example as a solid body, and is guided in ahousing hole 23 which extends parallel to the central longitudinal axisof the solenoid 21 and is prestressed into a position of rest by meansof a compression spring 24, in which position of rest it bears, in FIG.3, with its rear end wall against the left-hand end of the housing hole23. The other end wall of the armature 22 is acted on by the spring 24which is supported on the right-hand end of the hole 23 on the housingwall of the pump 11. The spring-loaded end side of the armature 22 ispermanently connected to a piston rod 25, to whose free end a piston 26,the delivery piston of the pump 11, is attached, which piston is guidedon the inner wall of the ram pipe 13 and is preferably sealed withrespect to this wall. The piston rod 25 penetrates a hole in the pumphousing, the diameter of which hole is smaller than the diameter of thehole guiding the armature 22.

[0026] The intake line 20 opens into the ram pipe 13 in front of the endface of the delivery piston 26 which is located on the outside. Thenonreturn valve 19 in the feed line 20 comprises, for example, aspring-prestressed sphere as a valve element, the sphere and springbeing arranged in such a way that the spherical valve element in thenonreturn valve is lifted off when the delivery piston 26 executes itsintake stroke in order to suck in fuel from the vessel 12, that is tosay when the piston 26 in FIG. 3 executes a stroke movement to the left,which is the case when the magnet 21 is deenergized and the armature 22is moved into its position of rest by the spring 24. In the other case,namely during the delivery stroke of the piston 26, corresponding to apiston movement in FIG. 3 to the right with the solenoid 21 excited, thevalve element of the nonreturn valve 20 is moved into its blockingposition, so that the connection of the ram pipe 13 to the reservoirvessel 12 is interrupted. The delivery stroke of the piston 26 causesthe mass of the fuel located in the ram pipe 13 to be accelerated andmoved, during an opening time period of the shut-off valve 16 which isprescribed by the control device 18, into the return line 17 and via itinto the vessel 12. During this time period, the fuel in the lines 13and 17 is therefore primarily accelerated, and the fuel pressure in thiscontext is so low that the nozzle 15 which is blocked in a manner knownper se, for example hydraulically, assumes a blocking state in which nofuel can escape via the nozzle.

[0027] If the quantity of fuel in the ram pipe 13 (and in the returnline 7) has reached an acceleration value prescribed by the controldevice 18 as a function of current engine operating conditions, theshut-off valve is closed, also under the control of the device 18, as aresult of which the kinetic energy of the fuel flowing in the lines 13and 14 is converted instantaneously into a quantity of pressure surgeenergy whose value is so high that the closing resistance of the nozzle15 is overcome and fuel is ejected via the nozzle 15. This fuelinjection device permits discontinuous operation of the piston pump,which pump, in conjunction with the electromagnetically actuatedshut-off valve 6, permits the injection process to be controlledprecisely.

[0028] These injection devices operating according to the energy storageprinciple are distinguished by injection pressures ≧40 bar, whichpressures preferably lie in a region around 60 bar. With an injectionpressure in the region of 60 bar, a fuel injection speed ofapproximately 50 m/s is achieved using conventional injection nozzles.The high injection pressures are produced in the form of pulses, thequantity of fuel injected per injection process being controlled by thelength of the injection pulses.

[0029] In the method according to the invention, the time for thetriggering or the start of the injection process is determined first.This can be done in a known manner by measuring a predetermined angularposition of the crankshaft. When the predetermined angular position isdetected, the injection procedure is triggered and at the same time atimer element is started, which after a predetermined time period, or apredetermined delay time, outputs a signal to ignite the fuel/airmixture in the combustion space.

[0030] While the timer element is measuring the predetermined delaytime, the following processes take place in the fuel injection device:

[0031] 1. the solenoid 21 is excited,

[0032] 2. the armature 22 and the fuel contained in the ram pipe 13 areaccelerated,

[0033] 3. the stored energy is transmitted to the fuel located in thepressure line 14,

[0034] 4. fuel is injected into the combustion space 4 when the closingresistance of the nozzle 15 has been overcome,

[0035] 5. the injected fuel is atomized and eddied in the combustionspace 4.

[0036] These processes which occur during the injection process aretime-invariant, i.e. the time period is predetermined or depends on afew parameters such as the quantity of fuel injected per injectionprocess, so that at the time when the injection process is triggered itis clear when the fuel injected into the combustion space 4 is in theideal state for an ignition.

[0037]FIG. 1 illustrates a small fuel cloud 28 for idling mode and alarge fuel cloud 29 for load mode. The ideal ignition time depends onhow the entire fuel cloud is distributed in the combustion space 4 andwhether a fuel/air mixture which is sufficiently rich for the ignitionhas become established in the region of a spark plug 30. The inventorshave found that the time for an ideal ignition, in particular duringidling, is obtained at a predetermined delay time with respect to thestart of the injection process, which delay time is dependent on only afew parameters.

[0038] The two-stroke internal-combustion engine to which the methodaccording to the invention has been applied has been equipped for directinjection with cylinder heads 31 and pistons 32, as illustrated in FIGS.4 and 5.

[0039]FIGS. 4 and 5 illustrate the pistons 32 in each case at the upperdead center, so that in each case a dome-shaped combustion space 4 isformed between the pistons 32 and the cylinder head 31. The fuel, whichforms an injection cone 33 in the combustion space 4, is injected intothis combustion space 4 using the injection nozzle 15.

[0040] In the embodiment according to FIG. 4, the spark plug 30 touchesthe injection cone 33, so that the injected jet of fuel can be igniteddirectly. In this embodiment, both direct injection and also directignition thus take place, since the directly injected jet of fuel isignited by the spark plug 30.

[0041] In the embodiment according to FIG. 5, the spark plug 30 does nottouch the injection cone 33. The injected fuel is reflected at thepiston 32 and only afterwards ignited by the spark plug 30. In thisembodiment therefore direct injection takes place, but no directignition.

[0042] Both embodiments are suitable for the time-delayed ignitionaccording to the invention.

[0043] In the embodiment with the direct ignition, the predeterminedtime period of the delay time lies in the region between 0.5milliseconds and 1 millisecond and during normal operation preferablyassumes a value of 0.7 milliseconds. The delay time is varied herepreferably as a function of the temperature of the internal combustionengine, the temperature being measured at the cylinder head 31. In thecase of a cold start, the delay time is set at approximately 0.5milliseconds, and in the case of a hot cylinder head 31 to 1millisecond. Further parameters for the setting of the delay timebetween the start of the injection process and the ignition time are nottaken into account. Such a method of controlling the ignition time canbe carried out easily and with little computational outlay, since thesuitable delay time is determined only as a function of a singleparameter, the cylinder head temperature.

[0044] With this embodiment, sensational synchronism in idling mode wasachieved so that the two-stroke internal combustion engine idlessmoothly even at a rotational speed of 180 rpm. This lowerrotational-speed limit of 180 rpm was prescribed merely by the controldevice used in the tests, since it is not capable of calculating anyslower rotational speeds.

[0045] Idling at a rotational speed of 180 rpm signifies a considerablesaving in fuel in comparison with customary idling speeds which are amultiple of the idling speed achieved here.

[0046] A very high degree of smoothness of running was also achievedwith the embodiment according to FIG. 5 in which the fuel is reflectedat the piston 32. Owing to the reflection of the fuel, the delay time islonger than in the case of direct ignition, the delay time lyingapproximately in the region between 3.5 milliseconds and 5.5milliseconds. It has become apparent that the delay time can be set to asingle constant value which lies preferably at approximately 4.5milliseconds. Such a constant delay time can be realized with verysimple technical means, it being unnecessary to use a microprocessor todo this.

[0047] The timer element can be realized both as a digital timer and asa simple hardware circuit (FIG. 6).

[0048] The hardware circuit is designed for a two-cylinder internalcombustion engine with in each case one input a, b to which the triggeror control signal for the injection process is applied. A controlvoltage which determines the delay time is applied to another input c.Given a constant delay time, the control voltage can be tapped at apotentiometer, and given a varying delay time the control voltage issupplied by the control device.

[0049] A positive rising edge of one of the trigger signals present ata, b switches a flip-flop 41, as a result of which the output Q of theflip-flop is energized. As a result, the output of a comparator 42 isopened, so that a capacitor 43 is charged via a resistor 44. The voltagepresent at the capacitor 43 is compared with a control voltage presentat a corresponding capacitor 45. If the voltages are of equal magnitude,the flip-flop 41 is reset, as a result of which a control signal for theignition is output at A, B.

[0050] The method according to the invention for controlling theignition time can also be combined with a conventional method forcontrolling the ignition time in which the ignition time is determinedas a function of a predetermined angular position of the crankshaft.Here, the method according to the invention is preferably applied belowa load threshold or rotational speed threshold and the conventionalmethod above this threshold. Such a rotational speed threshold liesapproximately in the region between 2000 and 4000 rpm.

[0051] In summary, it is noted that with the method of delayed ignitionaccording to the invention it is possible to determine the ignition timeusing simple technical means, excellent smoothness of running,particularly when idling, being achieved.

1. A method for controlling the ignition in a two-stroke internalcombustion engine having a high-pressure injection device for injectingfuel into a combustion space of the internal combustion engine atinjection pressures >40 bar, the fuel being directly injected into thecombustion space and mixing with the air located therein to form afuel/air mixture, an ignition time at which an ignition of the fuel/airmixture is carried out being determined above a specific load thresholdor rotational speed threshold by measuring a predetermined angularposition of the crankshaft, and below the rotational speed threshold acontrol signal for the injection process starting a measurement of apredetermined delay time, the expiry of which specifies the ignitiontime at which the control signal for the ignition is output.
 2. Themethod as claimed in claim 1, wherein the injection device used is aninjection device operating according to the energy storage principle. 3.The method as claimed in claim 2, wherein an injection device operatingaccording to the solid-state energy storage principle is used.
 4. Themethod as claimed in one or more of claims 1 to 3, wherein the time atwhich the injection process is triggered is determined by measuring apredetermined angular position of a crankshaft.
 5. The method as claimedin one or more of claims 1 to 4, wherein the predetermined delay time isconstant.
 6. The method as claimed in one or more of claims 1 to 4,wherein the predetermined delay time is determined in accordance withone or more parameters, such as the cylinder head temperature and/or thequantity of fuel injected per injection process.
 7. The method asclaimed in one or more of claims 1 to 6, wherein the fuel jet producedduring the injection is ignited directly.
 8. The method as claimed inclaim 7, wherein the predetermined delay time lies in the region between0.5 ms to 1 ms.
 9. The method as claimed in claim 8, wherein, after theinjection, the fuel is reflected at a piston and after the reflection itis ignited at the piston by a spark plug.
 10. The method as claimed inclaim 9, wherein the predetermined delay time lies in the region between3.5 to 5.5 ms.
 11. The method as claimed in claim 9 and/or 10, whereinthe fuel is reflected in a depression on the piston.
 12. The method asclaimed in one or more of claims 1 to 11, wherein, in order to measurethe predetermined delay time, a hardware circuit is provided which usesthe signal for triggering the injection process as a trigger signal formeasuring the predetermined delay time.
 13. The method as claimed in oneor more of claims 1 to 12, wherein the rotational speed threshold liesin the region between 2000 and 4000 rpm.